MULTIQUANT Report Summary

Quantum information processing (QIP) promises an exponential acceleration of certain computational tasks by encoding information as superposition states of a quantum system.

Over the past two decades, many physical systems have been considered for realizing QIP, from trapped ions to superconducting circuits. One of the leading schemes is linear optical quantum computation (LOQC), which uses photons as the information carriers. Photons have the advantages of being very robust against noise, easy to manoeuvre in space, can be shared between distant parties with little loss, and operate at ambient conditions.

Up to date, however, the experimental demonstrations of LOQC have used up to four photons. This is due to the non-deterministic, probabilistic generation of photons by means of nonlinear optics, rendering the probability of simultaneous emission to exponentially decay with the number of photons required. The exponential speed-up promised by QIP is thus cancelled-out. Truly deterministic, room-temperature, single photon sources (SPSs) of this scale are still unavailable.

MULTIQUANT was designed to address this very issue. The proposed strategy was the combination of non-deterministic SPSs and broad-band quantum optical memories (QOMs), for increasing the success rate using temporal multiplexing. The platform chosen was diamond, a solid-state material that can both guide light and host various point defects which can serve as both SPSs and QOMs.

Summary of the objectives of MULTIQUANT:

1. Training and Transfer of Knowledge:As stated in section B1, MULTIQUANT was designed to bring together a world class experimental and theoretical group in the field of quantum optics, the Ultrafast Quantum Optics and Optical Metrology Group, Oxford University, United Kingdom (UQOG), and the research fellow (IEF), Dr. E. Poem-Kalogerakis, an experienced researcher with wide experimental and theoretical expertise in the fields of solid-state physics, few interacting particles systems, coherent control, and quantum optics, as well as in numerical modelling.

As listed in section B2.1, MULTIQUANT focused on delivering multiple valuable training objectives to the IEF, aimed to broaden the area of his research expertise, to involve him in multidisciplinary activities in the areas of quantum optics, physics of complex systems, integrated optics, atomic physics, nanofabrication, and optical applications, to improve his experimentation skills, to deepen his experience in project management, and to expand greatly his network of contacts within experimental and theoretical physics, optical engineering and industry, placing him on the leading edge of the field of experimental quantum optics.

2. Scientific Discovery:As summarised in section B1.1.3, the key scientific aim was the creation and manipulation of correlated multi-photon states. Towards this goal, two major objectives were defined:1. The development of an all-solid-state, room-temperature, multi-channel, multi-photon source, composed of one SPS and several QOMs, aiming at channel and photon numbers as high as 10 or 12. 2. The manipulation of the emitted photons, using photonic circuits, into desired, highly correlated quantum states of light, and the detection of the resulting multi-photon correlations.

Work Summary:

Throughout MULTIQUANT, the IEF has facilitated knowledge transfer and has made considerable scientific progress under the leadership of the scientist in charge, Prof. Ian Walmsley (SIC), within the larger UQOG at the University of Oxford. Within the UQOG the IEF has created and led the solid-state memories subgroup, a team of 4 currently, which works as a part of the memories subgroup, led by Dr. Joshua Nunn.

The IEF has been involved in activities from leading and developing experimental efforts in the laboratory, formulating broader research directions, and data analysis, to scientific and public dissemination of our results, teaching undergraduate students, and co-supervising graduate students alongside the SIC.

In addition, the IEF has initiated and established two new scientific collaborations. One is between the UQOG and the C. Becher group at Saarlands University, Germany, aimed at opening another avenue for implementing QOMs in diamond. The other is between the UQOG and the Silberberg group at Weizmann Inst. Of Science, Israel, aimed at new applications of multi-mode, multi-photon states.

While leading the solid-state memory sub-team in the UQOG, the IEF has published four papers in international physics journals as a direct outcome of this work where the IEF was first author on one (see list below). In addition, a paper was published in collaboration with an Israeli research group, another paper is on the arXiv and under review in Phys. Rev. A, and three more (one is in collaboration with Saarlands University) are in preparation, expected to be completed and published in the next 4-8 months. Of these papers, the IEF will be a last author on one, and an equal contribution on another.